Rework createFile() to support systems where exclusive mode doesn't work.
Rework createFile() to support systems where exclusive mode doesn't work.

Jira issue: WP-902

This change is primarily for Android that doesn't yet support the new
exclusive-mode flags but other platforms are also potentially problematic.

krishnabangalore/Webinos-Platform,webinos/Webinos-Platform,webinos/Webinos-Platform,webinos/Webinos-Platform,krishnabangalore/Webinos-Platform,krishnabangalore/Webinos-Platform,webinos/Webinos-Platform,webinos/Webinos-Platform,krishnabangalore/Webinos-Platform,krishnabangalore/Webinos-Platform,krishnabangalore/Webinos-Platform,krishnabangalore/Webinos-Platform,webinos/Webinos-Platform,krishnabangalore/Webinos-Platform,webinos/Webinos-Platform,webinos/Webinos-Platform,webinos/Webinos-Platform,krishnabangalore/Webinos-Platform