fstests: install soak_duration.awk

fstests: install soak_duration.awk

Commit 3e85dd4fe423 ("misc: add duration for long soak tests") added a
helper executable, soak_duration.awk, is which used by the check
script if SOAK_DURATION is set.  This script translates a
"human-friendly" time duration specifier, such as 4m or 2d into an
integer number of seconds.  We need to make sure that this script is
installed or the check script will bomb out if SOAK_DURATION is set
(and if the fstests installation doesn't include a full set of fstests
source, but just those files installed by "make install").

Fixes: 3e85dd4fe423 ("misc: add duration for long soak tests")
Cc: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Zorro Lang <zlang@redhat.com>
Signed-off-by: Zorro Lang <zlang@kernel.org>