Support for all argument in upgrade plugin

[joshrotenberg]

Adds support for -a/--all to rebar3 plugins upgrade, replacing the no argument functionality with the all flag.

See #2583.

[joshrotenberg]

shelltests failed. Did I miss a test case somewhere?

[ferd]

shelltests failed. Did I miss a test case somewhere?

Shelltests are an external repo we have that validates integrations (https://github.com/tsloughter/rebar3_tests).

 Warning: Command:
rebar3 plugins
--- Expected
+++ Got
+   4   upgrade        Upgrade plugins.
-  23   upgrade        Upgrade plugins

:help_tests/help_tests.test:4: [Failed]
Warning: Command:
rebar3 help plugins
--- Expected
+++ Got
+   4   upgrade        Upgrade plugins.
-  31   upgrade        Upgrade plugins

The difference is a changed '.' in the output.