fix handling of config options that share the same prefix

container_config:
      - "lxc.network.ipv4.gateway=auto"
      - "lxc.network.ipv4=192.0.2.1"

might try to override lxc.network.ipv4.gateway in the second entry as both
start with "lxc.network.ipv4".
use a regular expression to find a line that contains (optional) whitespace
and an = after the key.

Signed-off-by: Evgeni Golov <evgeni@golov.de>

lib/ansible/modules/extras/cloud/lxc/lxc_container.py

@@ -424,6 +424,8 @@ lxc_container:
             sample: True
 """
 
+import re
+
 try:
     import lxc
 except ImportError:
@@ -748,9 +750,10 @@ class LxcContainerManagement(object):
             key = key.strip()
             value = value.strip()
             new_entry = '%s = %s\n' % (key, value)
+            keyre = re.compile(r'%s(\s+)?=' % key)
             for option_line in container_config:
                 # Look for key in config
-                if option_line.startswith(key):
+                if keyre.match(option_line):
                     _, _value = option_line.split('=', 1)
                     config_value = ' '.join(_value.split())
                     line_index = container_config.index(option_line)