Coverage: Adds option "COVERAGE=ON|OFF" to add "--coverage" flag for gcc

This commits add the "COVERAGE" option to cmake.
If set ON, code will be compiled with "--coverage".
At runtime, ganesha will prouce *.gcda file (if shutdown gently).
Those files can be used as input to gcov or lcov to produce coverage reports.

Signed-off-by: Philippe DENIEL <philippe.deniel@cea.fr>
Coverage: adding a "lcov" target

This commit add a "lcov" target. This target will exist only
is COVERAGE=ON and if lcov as been installed on the machine.

Signed-off-by: Philippe DENIEL <philippe.deniel@cea.fr>
FSAL_LUSTRE: removes unused field 'inode' in fsal_handle.

Signed-off-by: Philippe DENIEL <philippe.deniel@cea.fr>
FSAL_LUSTRE: adds fsdev to fsal_handle to avoid collision in cache_inode

This commit adds field "fsdev" to fsal_handle. This field holds the FS'devid
from stat() (field st_dev in struct stat). If various LUSTRE are mounted on
a single Ganesha, handle could collide in cache_inode hash. Such a change
avoid this.

Signed-off-by: Philippe DENIEL <philippe.deniel@cea.fr>