Resolve writer tango timeouts
Closes #2094 (closed)
Timeout on tango calls to the writer had nothing to do with blocking gevent. The solution was to cache some Redis queries.
Additional things:
- Add more resource profiling options to the writer (not just True or False, but WALL50, CPU100, MEM30, ...)
- NEXUS_WRITER_SESSION from the test suite has the ESRF data policy enabled default (as opposed to all other sessions in the test suite)