Extend RAPI client constant unit test with error codes
Extend RAPI client constant unit test with error codes

The RAPI client is meant to be independent from the wider Ganeti
codebase, but it still needs to use Ganeti constants. To enforce this,
a unit test is used. This patch extends the unit test with error code
messages, as these will be used in the commits to come.

Signed-off-by: Hrvoje Ribicic <be5828fca31f89218048bec4189e30a581aa65da@google.com>
Reviewed-by: Petr Pudlak <9d19625f8ee825a2c398462ed335cbcf98f79c32@google.com>

andir/ganeti,ganeti/ganeti,grnet/snf-ganeti,mbakke/ganeti,yiannist/ganeti,mbakke/ganeti,onponomarev/ganeti,leshchevds/ganeti,grnet/snf-ganeti,dimara/ganeti,andir/ganeti,ganeti/ganeti,apyrgio/ganeti,mbakke/ganeti,leshchevds/ganeti,bitemyapp/ganeti,yiannist/ganeti,yiannist/ganeti,andir/ganeti,apyrgio/ganeti,ganeti/ganeti,ganeti-github-testing/ganeti-test-1,ganeti-github-testing/ganeti-test-1,leshchevds/ganeti,bitemyapp/ganeti,dimara/ganeti,onponomarev/ganeti