This change adds support for executing ct test runs based on test specificiations, which was missing previously. The rebar_ct module now looks for any number of files with a name ending in `test.spec` and if it finds one or more, passes these after the `-spec` argument to ct_run instead of explicitly configuring the config, user config and coverage config variables. When no specifications are found, then the module behaves as it did before this change, and both the ct1 and (new) ct2 integration tests appear to show this is a backwards compatible patch.
…invoking the shell script. Also now using DRV_* env vars for compilation/linking of files found in c_src; this frees up "normal" CFLAGS/LDFLAGS for usage in sub build scripts.