raise timeout for priority takeover in replsets_priority1.js

replsets_priority1.js only waits 60 seconds for a priority takeover; however, when only two nodes of a three node set are up, and the higher priority node (in secondary state) is behind the lower priority node (in primary state), and the higher priority node's sync source was previously the third node (that is now down), it can take quite a while for the higher priority node to switch sync sources, catch up, and successfully run for election as a priority takeover.