Make environ.exp run on all platforms (and create info-program.exp)

Make environ.exp run on all platforms (and create info-program.exp)

This has been on my TODO list for a while.  There's a really old bug
about this (PR testsuite/8595), and there was no reason for
environ.exp to be specific for hppa* targets.  So this patch removes
this constraint, modernizes the testcase, and cleans up some things.
Most of the tests remained, and some were rewritten (especially the
one that checks if "show environment" works, which is something kind
of hard to do).

As a bonus, I'm adding a separated info-program.exp file containing
all the tests related to "info program" that were present on
environ.exp.

Tested locally, everything still passes.

gdb/testsuite/ChangeLog:
2017-04-28  Sergio Durigan Junior  <sergiodj@redhat.com>

	PR testsuite/8595
	* gdb.base/environ.exp: Make test available in all architectures.
	Move bits related to "info program" testing to
	gdb.base/info-program.exp.  Rewrite tests to use the two new
	procedures mentione below.
	(test_set_show_env_var) New procedure.
	(test_set_show_env_var_equal): Likewise.
	* gdb.base/info-program.exp: New file.