ip-up-vpn: Fix resource leaks in error cases

These leaks aren't really consequential since this is a standalone
command, and these "leaks" are in main().  But by putting in simple
fixes for these, we reduce the noise when using static analysis to
find leaks in Android code.

Test: TreeHugger
Change-Id: I2cbb4585c6c8d59a0eb89a72f17dfc4fbc532249