Bug 784816 - Adding upgradeToSecure() to support startTLS in MozTCPSocket. r=mayhemer sr=sicking a=blocking-b2g=leo+ from bug 914520

Uplift patch prepared by asutherland@asutherland.org.  Tested using xpcshell
tests and on unagi device running b2g18 with gaia v1-train and modified email
app.