Add --loglevel option to cluster_run.
Add --loglevel option to cluster_run.

It allows to specify wanted logging verbosity. So --loglevel=error
will print only error messages. If the option is omitted then
configuration is read from static_config.

Change-Id: I81ce3967457c3db1b294566903efed20a4569c18
Reviewed-on: http://review.couchbase.org/10591
Tested-by: Aliaksey Artamonau <3c875bcfb3adf2a65b2ae7686ca921e6c9433147@gmail.com>
Reviewed-by: Dale Harvey <491ccac09a36ad1e38b698f273b84fd8efc31071@arandomurl.com>
Tested-by: Dale Harvey <491ccac09a36ad1e38b698f273b84fd8efc31071@arandomurl.com>

ceejatec/ns_server,vzasade/ns_server,vzasade/ns_server,daverigby/ns_server,ceejatec/ns_server,ceejatec/ns_server,nimishzynga/ns_server,t3rm1n4l/ns_server,mschoch/ns_server,mschoch/ns_server,daverigby/ns_server,vzasade/ns_server,daverigby/ns_server,t3rm1n4l/ns_server,nimishzynga/ns_server,ceejatec/ns_server,daverigby/ns_server,mschoch/ns_server,t3rm1n4l/ns_server,nimishzynga/ns_server,daverigby/ns_server,membase/ns_server,ceejatec/ns_server,membase/ns_server,membase/ns_server,ceejatec/ns_server,pavel-blagodov/ns_server,t3rm1n4l/ns_server,nimishzynga/ns_server,vzasade/ns_server,membase/ns_server,t3rm1n4l/ns_server,pavel-blagodov/ns_server,pavel-blagodov/ns_server,pavel-blagodov/ns_server,membase/ns_server,mschoch/ns_server,nimishzynga/ns_server,nimishzynga/ns_server,mschoch/ns_server,membase/ns_server,mschoch/ns_server