Improve RESTCONF QName parsing speed

SchemaContext provides useful (and optimized) methods for looking up
modules. Eliminate home-grown version of findModuleByName(). Requires
https://git.opendaylight.org/gerrit/#/c/9351/ .

Change-Id: I4c4e07e23a614b46b01a87485965af0c066aa693
Signed-off-by: Robert Varga <rovarga@cisco.com>
Merge "Improve RESTCONF QName parsing speed"