LU-1943 test: Support --with-ldiskfsprogs in test framework

ORI-347 port to the master

When Lustre is built with the --with-ldiskfsprogs option the
Lustre utilities will expect to find the e2fsprogs utilties
repackaged as ldiskfsprogs on the system.  This is done to
avoid having to replace the distribution provided e2fsprogs
package.

This change extends the test framework to check for the
ldiskfsprogs utilties to avoid having to explicitly set
the shell variables when --with-ldiskfsprogs is used.
If the tools are not available it will fallback to using
the e2fsprogs utilities.

Signed-off-by: Prakash Surya <surya1@llnl.gov>
Signed-off-by: Mikhail Pershin <tappro@whamcloud.com>
Change-Id: Ia094d9b005f7e455beca1c5d6d6ad03bdc03671f
Reviewed-on: http://review.whamcloud.com/4194
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Alex Zhuravlev <bzzz@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>