avoid crash when overlay is malformed

[sg2342]

• handle invalid overlay entries in do_individual_overlay/4
• raise error exception when do_overlay/4 returns {error, _}
• add format_error/1 clauses for 'unable_to_chmod' and 'link_failed'

fix: #867

[sg2342]

i amended the PR to format link_failed and unable_to_chmod errors.
without it, rebar3 would throw 'no function clause matching' exceptions on these.

[sg2342]

With the PR merged and included in a rebar3 release; the rebar3 release task behavior will change (with examples taken from the shelltest in #917):

1 malformed_overlay

anything not understood by relx_overlay, e.g.
{overlay, [{malformed, foo}]}

1.1 BEFORE merge: crash

rebar3 release fails (exit code 1), error output:

===> Uncaught error in rebar_core. Run with DIAGNOSTIC=1 to see stacktrace or consult rebar3.crashdump

1.2 AFTER merge

rebar3 release succeeds (exit code 0), error output:

===> Overlay section malformed: {malformed,foo}

2 unable_to_make_dir

failure to create a directory, e.g.
{overlay, [{mkdir, "releases/RELEASES"}]}

2.1 BEFORE merge: silent faiure

rebar3 release succeeds (exit code 0), no error output.

2.2 AFTER merge

rebar3 release fails (exit code 1), error output:

===> Unable to make directory /tmp/relx/shelltests/overlay_error_test/_build/mkdir_error/rel/overlay_error_test/releases/RELEASES because eexist

3 copy_failed

failure to copy file, e.g.
{overlay, [{copy, "does_not_exist", "something"}]}

3.1 BEFORE merge: silent failure, tar task behaves different

• rebar3 release succeeds (exit code 0), no error output.
• however, rebar3 tar will fail (exit code 1) with error output

===> Tarball generation errors:
Cannot add file /tmp/relx/shelltests/overlay_error_test/_build/copy_error/rel/overlay_error_test/something to tar file - /tmp/relx/shelltests/overlay_error_test/_build/copy_error/rel/overlay_error_test/something: no such file or directory

3.2 AFTER merge

rebar3 release fails (exit code 1), error output:

===> Unable to copy from /tmp/relx/shelltests/overlay_error_test/does_not_exist to /tmp/relx/shelltests/overlay_error_test/_build/copy_error/rel/overlay_error_test/something because of {copy_failed,
                                                                                                                                                                                                         "/tmp/relx/shelltests/overlay_error_test/does_not_exist",
                                                                                                                                                                                                         "/tmp/relx/shelltests/overlay_error_test/_build/copy_error/rel/overlay_error_test/something",
                                                                                                                                                                                                        enoent}

4 read_template

failure to read a template file e.g.
{overlay, [{template, "does_not_exist", "something"}]}

4.1 BEFORE merge: silent failure, tar task behaves different

• rebar3 release succeeds (exit code 0), no error output.
• however, rebar3 tar will fail (exit code 1) with error output

===> Tarball generation errors:
Cannot add file /tmp/relx/shelltests/overlay_error_test/_build/template_read_error/rel/overlay_error_test/something to tar file - /tmp/relx/shelltests/overlay_error_test/_build/template_read_error/rel/overlay_error_test/something: no such file or directory

4.2 AFTER merge

rebar3 release fails (exit code 1), error output:

===> Unable to read template file (/tmp/relx/shelltests/overlay_error_test/does_not_exist) for overlay due to: no such file or directory

5 write_template

failure to write a templated file e.g.
{overlay, [{template, "README.md", "releases"}]}

5.1 BEFORE merge: silent failure

rebar3 release succeeds (exit code 0), no error output.

5.2 AFTER merge

rebar3 release fails (exit code 1), error output:

===> Unable to write to /tmp/relx/shelltests/overlay_error_test/_build/template_write_error/rel/overlay_error_test/releases because eisdir

6 template_dir

failure to create a enclosing directory e.g.
{overlay, [{template, "README.md", "releases/RELEASES/foo"}]}

6.1 BEFORE merge: silent failure, tar task behaves different

• rebar3 release succeeds (exit code 0), no error output.
• however, rebar3 tar will fail (exit code 1) with error output

===> Tarball generation errors:
Cannot add file /tmp/relx/shelltests/overlay_error_test/_build/template_dir_error/rel/overlay_error_test/releases/RELEASES/foo to tar file - /tmp/relx/shelltests/overlay_error_test/_build/template_dir_error/rel/overlay_error_test/releases/RELEASES/foo: not a directory

6.2 AFTER merge

rebar3 release fails (exit code 1), error output:

===> Unable to create enclosing directory for /tmp/relx/shelltests/overlay_error_test/_build/template_dir_error/rel/overlay_error_test/releases/RELEASES/foo because eexist

7 chmod_error

failure to modify file mode bits e.g.
{overlay, [{chmod, 0, "does_not_exist"}]}

7.1 BEFORE merge: silent failure

rebar3 release succeeds (exit code 0), no error output.

7.1 AFTER merge

rebar3 release fails (exit code 1), error output:

===> Unable to chmod 0 does_not_exist because of enoent

8 link_error

failure to create a symbolic link.
It is surprisingly hard to get rlx_overlay:link_to/4 to fail...

 {mode, dev},
 {overlay, [{link, "README.md", "../../../../../../../../../../../../../../../../../../../../../../../../f"}]}

8.1 BEFORE merge: silent failure, tar task behaves different

• rebar3 release succeeds (exit code 0), no error output.
• however, rebar3 tar will fail (exit code 1) with error output

===> Tarball generation errors:
Cannot add file /tmp/relx/shelltests/overlay_error_test/_build/link_error/rel/overlay_error_test/../../../../../../../../../../../../../../../../../../../../../../../../f to tar file - /tmp/relx/shelltests/overlay_error_test/_build/link_error/rel/overlay_error_test/../../../../../../../../../../../../../../../../../../../../../../../../f: no such file or directory

8.2 AFTER merge

rebar3 release fails (exit code 1), error output:

===> Unable to symlink /tmp/relx/shelltests/overlay_error_test/README.md to /tmp/relx/shelltests/overlay_error_test/_build/link_error/rel/overlay_error_test/../../../../../../../../../../../../../../../../../../../../../../../../f because of eacces