extended ServersSection#postAndReload for better error handling
extended ServersSection#postAndReload for better error handling

Particularly errorMessage argument can be a function that will be
handled when post fails.

Change-Id: I7451724e5663502b3d9d39863a3d5e2b89de2dca
Reviewed-on: http://review.couchbase.org/10142
Tested-by: Aliaksey Kandratsenka <340b8e09ca65cd3fc686427fcfed17e87eaf61e2@gmail.com>
Reviewed-by: Aliaksey Artamonau <3c875bcfb3adf2a65b2ae7686ca921e6c9433147@gmail.com>
Reviewed-by: Farshid Ghods <e312e45b3dfe8923eeb42f1475810bf7c59ba895@gmail.com>
Tested-by: Farshid Ghods <e312e45b3dfe8923eeb42f1475810bf7c59ba895@gmail.com>

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