util: command: Ignore bitmap errors when enumerating file descriptors to close

virCommandMassCloseGetFDsLinux fails when running libvird on valgrind
with the following message:

libvirt: error : internal error: unable to set FD as open: 1024

This is because valgrind opens few file descriptors beyond the limit:

65701125 lr-x------. 1 root root 64 Jul 18 14:48 1024 -> /home/pipo/build/libvirt/gcc/src/.libs/libvirtd
65701126 lrwx------. 1 root root 64 Jul 18 14:48 1025 -> '/tmp/valgrind_proc_3849_cmdline_186612e3 (deleted)'
65701127 lrwx------. 1 root root 64 Jul 18 14:48 1026 -> '/tmp/valgrind_proc_3849_auxv_186612e3 (deleted)'
65701128 lrwx------. 1 root root 64 Jul 18 14:48 1027 -> /dev/pts/11
65701129 lr-x------. 1 root root 64 Jul 18 14:48 1028 -> 'pipe:[65689522]'
65701130 l-wx------. 1 root root 64 Jul 18 14:48 1029 -> 'pipe:[65689522]'
65701131 lr-x------. 1 root root 64 Jul 18 14:48 1030 -> /tmp/vgdb-pipe-from-vgdb-to-3849-by-root-on-angien

Ignore bitmap errors in this case since we'd leak those FD's anyways in
the previous scenario.

Signed-off-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: Michal Privoznik <mprivozn@redhat.com>