Description of problem:
Cloning a channel via API fails if channel label starts with a digit.

The problem is that the regular expression that verifies the channel label when the channel is cloned via API is not correct: 
 Pattern.compile("^[a-z][a-z\\d\\-\\.\\_]*$", Pattern.CASE_INSENSITIVE); 

The correct one is the one used when the channel is cloned on WebUI:
$channel_label =~ /^[a-z\d][a-z\d\-\.\_]*$/

Version-Release number of selected component (if applicable):
spacewalk-java-2.1.28-1

How reproducible:
100

Steps to Reproduce:
1. Execute the following script.

import sys, xmlrpclib
RHN_SERVER='https://xxxx.redhat.com/rpc/api'
RHN_USER='xxxx'
RHN_PASS='xxxx'
client = xmlrpclib.Server(RHN_SERVER, verbose=0)
key = client.auth.login(RHN_USER, RHN_PASS)

client.channel.software.create(key,'test_label','test_name','summary','channel-x86_64','')
client.channel.software.clone(key,'test_label',{'name':'clone-test_name','label':'222clone-test_label','summary':'test summary',},True)


Actual results:
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib64/python2.7/xmlrpclib.py", line 1224, in __call__
    return self.__send(self.__name, args)
  File "/usr/lib64/python2.7/xmlrpclib.py", line 1578, in __request
    verbose=self.__verbose
  File "/usr/lib64/python2.7/xmlrpclib.py", line 1264, in request
    return self.single_request(host, handler, request_body, verbose)
  File "/usr/lib64/python2.7/xmlrpclib.py", line 1297, in single_request
    return self.parse_response(response)
  File "/usr/lib64/python2.7/xmlrpclib.py", line 1473, in parse_response
    return u.close()
  File "/usr/lib64/python2.7/xmlrpclib.py", line 793, in close
    raise Fault(**self._stack[0])
xmlrpclib.Fault: <Fault -1: "redstone.xmlrpc.XmlRpcFault: unhandled internal exception: The channel parameter 222clone-test_label is invalid. It Must  be at least 6 characters long, begin with a letter, and contain only lowercase letters, digits, '-', '_', and '.'.  Also, it cannot begin with 'rhn', 'redhat', or 'red hat'.">


Expected results:
The channel is cloned successfully as it will happen if the same action was done on WebUI.

Additional info: