v2v: Remove useless parentheses around expression.
v2v: vmware: Use 'curl --config' to pass arguments securely to curl.

Instead of making up an ordinary curl command line, write a temporary
config file and use 'curl --config tmpfile' to pass the arguments.

The advantage is that it's more secure if we want to supply passwords
to curl, since a '--user username:password' parameter on the command
line could be read (eg. by 'ps ax'), but the temporary file has mode
0600 and cannot be read by other users.

This is mostly code motion, but it also passes the '-q' option to curl
to stop it from reading default configuration files.
v2v: Add --password-file parameter (RHBZ#1158526).

This allows you to send passwords to virt-v2v input modes without
being interactive.