[acceptance-tests] Fix tarball build and rename "check" target to "check-full"

[acceptance-tests] Fix tarball build and rename "check" target to "check-full"

The acceptance-tests folder wasn't getting included in the tarball, adding the folder
to the SUBDIRS in the top-level Makefile.am fixes this. Additionally, EXTRA_DISTFILES
doesn't work outside of mcs/ so rename it to EXTRA_DIST.

Since we don't want a top-level "make check" to recurse into acceptance-tests just yet,
rename the check target to check-full so nothing gets run by default.