Add support for --trust-server-cert in SVN provider

Added suport for SVN provider's parameter "--trust-server-cert".

This parameter tells svn client to ignore the "issuer not trusted" errors when using an HTTPS repository. If it is not specified the module behaves as usual.

Usage:
vcsrepo {"my repo":
	ensure => latest,
	provider => svn,
	source => "https://svn.example.com/svn/myproject/trunk",
	basic_auth_username => 'myusername',
	basic_auth_password => 'mypassword',
	trust_server_cert => true,
}