tools/cgxset: add -R option to recursively set variables

tools/cgxset: add -R option to recursively set variables

Add -R option to recursively set variable(s) passed to cgroups under
<cgroup_path>. This will help users to set a controller setting for
all the cgroups under a cgroup hierarchy, instead of passing the
cgroups multiple times on the command line.

example:
--------
./cgcreate -gcpu,memory:foo -gcpu:memory:foo/ch1 -gcpu,memory:foo/ch2
./cgget -r cpu.shares foo foo/ch1 foo/ch2
foo:
cpu.shares: 1024

foo/ch1:
cpu.shares: 1024

foo/ch2:
cpu.shares: 1024

Without the patch
------------------
./cgxset -2 -r cpu.weight=256 foo
./cgget -r cpu.shares foo
foo/ch1 foo/ch2
foo:
cpu.shares: 256

foo/ch1:
cpu.shares: 1024

foo/ch2:
cpu.shares: 1024

With the patch
--------------
./cgxset -R -2 -r cpu.weight=50 foo
./cgget -r cpu.shares foo foo/ch1 foo/ch2
foo:
cpu.shares: 512

foo/ch1:
cpu.shares: 512

foo/ch2:
cpu.shares: 512

Signed-off-by: Kamalesh Babulal <kamalesh.babulal@oracle.com>
Signed-off-by: Tom Hromatka <tom.hromatka@oracle.com>