Fixed ext storage webdav path encoding

- Some WebDAV servers like lighttpd need paths in URLs to be properly
encoded
- Added error log output when curl connection failed
- Added check for 'resourcetype' in case the WebDAV server doesn't
  support/return it
- Fixed touch() to return false if the server doesn't implement
  PROPPATCH
- Added optional delay in WebDAV unit tests to use when testing against
  lighttpd's WebDAV
Merge pull request #7027 from owncloud/extstorage-webdavurlencodingfixes

Fixed ext storage webdav path encoding