COMMONS-339: [UserStateService]: getUserState() failed when checking use...

...r status

Problem analysis:
* exo:lastActivity stores user's last access in milliseconds. It is a long value.
* In legacy data where user state cannot be updated due to the previous parsing error, it lacks exo:status property in the VideoCall node.

Fix description:
* Correct the way to parse exo:lastActivity value.
* When exo:status is missing, it will be set with the default value (available).