Update test_offline.py

[gaurimakhija]

Problem: The string "is alive!" is unlikely to appear in the output of a ping command. Typically, the output will contain something like "bytes from ..." or "time=" in successful pings. Fix: Check for actual ping response patterns, such as "bytes from" or "time="

Summary by CodeRabbit

• Tests
  • Improved connectivity check logic in offline smoke tests for enhanced reliability.