URLs downloaded with cURL should be stripped of newlines

Following on from the recent fix in cURL to address CVE-2014-8150, cURL rejects URLs with newline characters in them.

The landscape charm is currently failing with a hook error because by virtue of the include-file:// directives newline character is at the end of the license-file config value.

2015-01-15 17:32:22 INFO juju-log Fetching License: http://my.server/license.txt

2015-01-15 17:32:22 INFO config-changed Traceback (most recent call last):
2015-01-15 17:32:22 INFO config-changed File "/var/lib/juju/agents/unit-landscape-msg-0/charm/hooks/config-changed", line 908, in <module>
2015-01-15 17:32:22 INFO config-changed hooks[hook]()
2015-01-15 17:32:22 INFO config-changed File "/var/lib/juju/agents/unit-landscape-msg-0/charm/hooks/config-changed", line 492, in config_changed
2015-01-15 17:32:22 INFO config-changed _install_license()
2015-01-15 17:32:22 INFO config-changed File "/var/lib/juju/agents/unit-landscape-msg-0/charm/hooks/config-changed", line 562, in _install_license
2015-01-15 17:32:22 INFO config-changed license_file = _download_file(license_file)
2015-01-15 17:32:22 INFO config-changed File "/var/lib/juju/agents/unit-landscape-msg-0/charm/hooks/config-changed", line 511, in _download_file
2015-01-15 17:32:22 INFO config-changed curl.perform()
2015-01-15 17:32:22 INFO config-changed pycurl.error: (3, 'Illegal characters found in URL')