Improve RESTCONF thread safety when reconfiguring

There is a race which could see us without a populated mapping while a
schemacontext change is underway. Use a immutablemap guarded by an
atomicreference to allow proper switching. Note that the fix is
incomplete, as the schema context needs to be replaced at the same time.

Change-Id: I7d64fae99a0bc0f7d1ec19f08450c1954cb7af97
Signed-off-by: Robert Varga <rovarga@cisco.com>
Optimize RESTCONF module/node parsing

Profiling has shown that the current implementations are still not upto
par with what they should be: 189 invocations of the two consumed 64ms,
with most of the time being spent splitting and iterating.

Given that the parsing operation is really simple, we can do much better
using String.indexOf() and String.substring().

Change-Id: I06ef0403edb2c8d12cbbc3c7909091e9efc5138e
Signed-off-by: Robert Varga <rovarga@cisco.com>
Merge "Improve RESTCONF thread safety when reconfiguring"
Merge "Optimize RESTCONF module/node parsing"