Output boot code warning when zpool upgrade -a is used to add features.

In the case where new features where enabled by a zpool upgrade -a the
boot code warning wasn't output.

Submitted by:	Jan Kokemueller
MFC after:	3 days
sh(1): Clarify that assignments before commands do not affect expansions.

PR:		193759
MFC after:	1 week
Add some ATF tests for libproc.

Differential Revision:	D710
Reviewed by:	jmmv, ngie, rpaulo
Ignore a test program which doesn't compile at the moment. It will be
addresed properly when integrating the DTrace tests with Kyua.