testscripts/test_robind.sh: cleanup and make some fixes

Remove useless comments and abandon the operation which creates
a 500MB image-file. If user wants to run these tests, a big block
device should be specified by running runltp with -z option.

And we split tests in testscripts/fs_ro_tests into separate testcases,
keep one entry per test in runtest/fs_readonly

Using the interface provided by the shell library test.sh.

Delete fs_ro_tests, which is not used now.

Fix bashishm.

Signed-off-by: Xiaoguang Wang <wangxg.fnst@cn.fujitsu.com>
Signed-off-by: Cyril Hrubis <chrubis@suse.cz>
test_robind.sh: Move the script to testcases/ dir

Move the test_robind.sh from testscripts to testcases/kernel/fs_readonly

This fixes the newly added fs_readonly runtest file.

Signed-off-by: Cyril Hrubis <chrubis@suse.cz>