Avoid leaking data from the kernel environment: When we convert the
initial static environment to a dynamic one, zero the static environment
buffer, and zero individual values when kern_unsetenv and freeenv are
called.

Tested by:	kmoore (VM memory dump + grep)
Tested by:	cperciva (kernel panic dump + grep)


git-svn-id: svn+ssh://svn.freebsd.org/base/head@273487 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f
Fix some buglets in the error-handling of getdevice(). In particular, report
an error if the argument to pciconf -a doesn't have a unit number, rather
than triggering an assertion failure.

PR:		194506
Reported by:	Anthony Cornehl <accornehl@gmail.com>
Sponsored by:	EMC / Isilon Storage Division


git-svn-id: svn+ssh://svn.freebsd.org/base/head@273488 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f