Extends use of ServiceProxy to more methods in HostAPI in cells

Cells prepend full cell path to the service ID before returning any
service related info. This means service ID is non numeric and can't
be cast into Service objects.  In cells, service_get_all method
in HostAPI (which is used to display list of services) strips out
the cell path from received IDs, creates Service objects using
remaining numerical ID and uses a ServiceProxy to associate cell paths
Service objects.
However, other service related methods do not do so. They include:
 - service_update (Used for enabling/disabling services)
 - service_get_all_by_host (Used for evacuation)
These functions try to cast received service info (with alphanumeric
service IDs) into Service objects and fail with a ValueError.
This leads to API cell throwing Error 500 for service-enable,
service-disable and evacuate.
This patch extends the ServiceProxy usage to both these methods. It
also changes the corresponding HostAPI tests.

Change-Id: Iff2707602d5fabfbe8438150b5ad74b3c31bb011
Closes-Bug: 1361180
Merge "Extends use of ServiceProxy to more methods in HostAPI in cells"