ykushcmd: Add string support to ykushcmd command

By default ykushcmd command supports option to [on, off, cycle] whole
ykush yepkit.
> ykushcmd -u a  # 'a' stands for all ports
> ykushcmd -d a  # 'a' stands for all ports
In current build only int is supported for port number, changing it
to string allows to control power on all ports with one command instead
of 3 if there are 3 ports.

Signed-off-by: Redzynia, MateuszX <mateuszx.redzynia@intel.com>

labgrid/resource/ykushpowerport.py

@@ -11,10 +11,10 @@ class YKUSHPowerPort(Resource):
 
     Args:
         serial (str): serial of the YKUSH device
-        index (int): port index"""
+        index (str): port index"""
     serial = attr.ib(validator=attr.validators.instance_of(str))
-    index = attr.ib(validator=attr.validators.instance_of(int),
-                    converter=int)
+    index = attr.ib(validator=attr.validators.instance_of(str),
+                    converter=str)
 
 @target_factory.reg_resource
 @attr.s(eq=False)
@@ -23,7 +23,7 @@ class NetworkYKUSHPowerPort(NetworkResource):
 
     Args:
         serial (str): serial of the YKUSH device
-        index (int): port index"""
+        index (str): port index"""
     serial = attr.ib(validator=attr.validators.instance_of(str))
-    index = attr.ib(validator=attr.validators.instance_of(int),
-                    converter=int)
+    index = attr.ib(validator=attr.validators.instance_of(str),
+                    converter=str)