LU-9798 tests: split server recovery tests

The Lustre test suite recovery-mds-scale has two tests; one
that fails over MDSs and a second test that fails over OSSs.
The default time for each of these tests to run is 24 hours.

Break up the two server recovery tests into separate test
suites so that they can be run independent of each other and
in parallel.

Collect commmon functions and global variables into a libary
used by all the recovery-*scale tests.

Test-Parameters: trivial env=SLOW=no,FAILURE_MODE=HARD \
iscsi=1 clientcount=4 osscount=2 ostcount=7 mdscount=2 \
mdtcount=2 austeroptions=-R failover=true \
testlist=recovery-mds-scale,recovery-oss-scale,recovery-random-scale

Signed-off-by: Alex Deiter <adeiter@tintri.com>
Change-Id: I4eda5265742270821fa10ab24f0e0637c00059d7
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/43461
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>