Remove $FreeBSD$: one-line sh pattern

Remove /^\s*#[#!]?\s*\$FreeBSD\$.*$\n/

Unbreak geli/gmirror testcases if their geom classes cannot be loaded

The problem with the logic prior to this commit was twofold:

1. The wrong set of idioms (TAP-compatible) were being applied to the ATF
testcases when run, resulting in confusing ATF failure results on setup.
2. The cleanup subroutines were broken when the geom classes could not be
loaded as they exited with 0 unexpectedly.

This commit changes the test code to source the class-specific configuration
(conf.sh) once globally, instead of sourcing it per testcase and per cleanup
subroutine, and to call the ATF-specific setup subroutine(s) inline in
the testcases.

The refactoring done is effectively a no-op for the TAP testcases, modulo
any refactoring done to create common code between the ATF and TAP
testcases.

This unbreaks the geli testcases converted to ATF in r327662 and r327683,
and the gmirror testcases added in r327780, respectively, when the geom
class could not be loaded.

tests/sys/geom/class/mirror/...
While here, ignore errors when turning debug failpoint sysctl off, which
could occur if the gmirror class was not loaded.

Submitted by: ngie
MFC after: 2 weeks
Pull Request: https://github.com/freebsd/freebsd/pull/241

Remove the executable bit from some recently added test scripts.

geli: optimize tests

Reduce the geli tests' runtime by about a third:

* In integrity_test:copy, use a file-backed md(4) device instead of a
malloc'd one. That way we can corrupt the underlying storage without
needing to detach and reattach the geli device.

* In integrity_test:{copy, hmac, data} and onetime_test:{onetime,
onetime_a}, move reads of /dev/random out of the loop.

MFC after: 2 weeks

geli: convert most tests from TAP to ATF

I'm leaving readonly_test and nokey_test alone for now. In a future commit
they should be broken up into several smaller test cases and distributed
between multiple files.

Reviewed by: ngie
MFC after: 2 weeks
Differential Revision: https://reviews.freebsd.org/D13717