LU-11607 tests: remove duplicate code lnet-selftest

LU-11607 tests: remove duplicate code lnet-selftest

lnet-selftest.sh and test-framework.sh both have a function
called is_mounted() that check if the file system is
mounted.  Since both functions do and return the same
thing, let's remove the is_mounted() function from
lnet-selftest.

Test-Parameters: trivial
Test-Parameters: fstype=zfs testlist=lnet-selftest,lnet-selftest
Test-Parameters: fstype=ldiskfs testlist=lnet-selftest,lnet-selftest
Signed-off-by: James Nunez <jnunez@whamcloud.com>
Change-Id: I05ce84002cfa8ac96ac4f1e8169fb2233b66f378
Reviewed-on: https://review.whamcloud.com/36965
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Serguei Smirnov <ssmirnov@whamcloud.com>
Reviewed-by: James Simmons <jsimmons@infradead.org>
Reviewed-by: Oleg Drokin <green@whamcloud.com>