utime: fix narrowing conversion compiler warning in sleep()

Fix compiler warning:
./include/utime.h: In member function 'void utime_t::sleep()':
./include/utime.h:139:50: warning: narrowing conversion of
 '((utime_t*)this)->utime_t::tv.utime_t::<anonymous struct>::tv_sec' from
 '__u32 {aka unsigned int}' to '__time_t {aka long int}' inside { } is
 ill-formed in C++11 [-Wnarrowing]
./include/utime.h:139:50: warning: narrowing conversion of
 '((utime_t*)this)->utime_t::tv.utime_t::<anonymous struct>::tv_nsec' from
 '__u32 {aka unsigned int}' to 'long int' inside { } is
 ill-formed in C++11 [-Wnarrowing]

Signed-off-by: Danny Al-Gaaf <danny.al-gaaf@bisect.de>
rbd: don't ignore return value of system()

Check for the return value of system() and handle the error if needed

Signed-off-by: Danny Al-Gaaf <danny.al-gaaf@bisect.de>
configure: fix check for fuse_getgroups()

Check for fuse_getgroups() only in case we have found libfuse already.
Moved the check to the check for --with-fuse.

Small fix: fix string for NO_ATOMIC_OPS, don't use "'".

Signed-off-by: Danny Al-Gaaf <danny.al-gaaf@bisect.de>
rbd-fuse: fix usage of conn->want

Fix usage of conn->want and FUSE_CAP_BIG_WRITES. Both need libfuse
version >= 2.8. Encapsulate the related code line into a check for
the needed FUSE_VERSION as already done in ceph-fuse in some cases.

Signed-off-by: Danny Al-Gaaf <danny.al-gaaf@bisect.de>
rbd-fuse: fix printf format for off_t and size_t

Fix printf format for off_t and size_t to print the same on 32 and 64bit
systems. Use PRI* macros from inttypes.h.

Signed-off-by: Danny Al-Gaaf <danny.al-gaaf@bisect.de>