cnode-metadata: Adds metadata field to capability/cnode/slot.

Motivation: The libcap user may want to associate some contextual
information for each capability (rather than with the object). For
example, the LCD microkernel uses metadata to track whether a page
referred to by a page capability has been mapped and where.

This metadata field *is not* carried over to child capabilities
during grant, and is NULL'd out when a capability is deleted from
a cspace (so when the slot is used again, the field starts out as
NULL).

Internals note: The cnode will start out with NULL metadata as well
when it is first used because we do a zalloc to create cnode tables.
1 job for master
Status Job ID Name Coverage
  Test
failed #140
testing

00:00:15

 
Name Stage Failure
failed
testing Test There is an unknown failure, please try again
make[3]: *** [_module_/home/gitlab_ci_multi_runner/builds/eda34605/0/xcap/libcap/build/src/kernel] Error 2
make[3]: Leaving directory `/usr/src/linux-headers-3.13.0-33-generic'
make[2]: *** [all] Error 2
make[2]: Leaving directory `/home/gitlab_ci_multi_runner/builds/eda34605/0/xcap/libcap/build/src/kernel'
make[1]: *** [all-recursive] Error 1
make[1]: Leaving directory `/home/gitlab_ci_multi_runner/builds/eda34605/0/xcap/libcap/build/src'
make: *** [all-recursive] Error 1

ERROR: Build failed with: exit status 1