Description of problem:
When activating a Satellite server with rhn-satellite-activate, and the path to a manifest file is entered with a tilde (~) for a home directory, the path is not expanded and the manifest is not found by activation command.

Version-Release number of selected component (if applicable):
spacewalk-backend-tools-2.5.3-111.el6sat

How reproducible:
always

Steps to Reproduce:
1. Place the manifest file in your home dir
2. 
# ls -lh ~/manifest.zip 
-rw-r--r--. 1 root root 424K Apr 24 09:24 /root/manifest.zip
# rhn-satellite-activate --manifest=~/manifest.zip

ERROR: unhandled exception occurred:
Traceback (most recent call last):
  File "/usr/bin/rhn-satellite-activate", line 38, in <module>
    sys.exit(abs(mod.main() or 0))
  File "/usr/lib/python2.6/site-packages/spacewalk/satellite_tools/rhn_satellite_activate.py", line 488, in main
    cdn_activate = cdn_activation.Activation(options.manifest)
  File "/usr/lib/python2.6/site-packages/spacewalk/cdn_tools/activation.py", line 37, in __init__
    self.manifest = Manifest(manifest_path)
  File "/usr/lib/python2.6/site-packages/spacewalk/cdn_tools/manifest.py", line 60, in __init__
    top_zip = zipfile.ZipFile(zip_path, 'r')
  File "/usr/lib64/python2.6/zipfile.py", line 683, in __init__
    self.fp = open(file, modeDict[mode])
IOError: [Errno 2] No such file or directory: '~/manifest.zip'

Actual results:
Path is not expanded and manifest file is not found.

Expected results:
Path is expanded and manifest file is successfully opened.

Additional info:
Same problem when using ~username shortut, for example "~root/manifest.zip"