Fixes for DWS GCE support

[Michaelvll]

This is to fix the DWS GCE support.

Disabled: STOP and SPOT_INSTANCES for now, as MIG with DWS does not support stopping a machine.

TODOs:

Single node

• sky launch -c test-mig --cloud gcp --cpus 2 --gpus t4 nvidia-smi
• sky stop test-mig (skip)
• sky down test-mig
• sky autostop -i 0 test-mig (skip)
• sky status -r test-mig
• sky start -f test-mig
• sky autostop -i 0 --down test-mig
• sky status -r test-mig

Multiple nodes

• sky launch -c test-mig-mn --num-nodes 4 --cloud gcp --cpus 2 --gpus t4 nvidia-smi
• sky stop test-mig-mn (skip)
• sky autostop -i 0 test-mig-mn (skip)
• sky status -r test-mig-mn
• sky start -f test-mig-mn
• sky autostop -i 0 --down test-mig-mn
• sky down test-mig-mn

Multiple spot nodes

• sky launch --cloud gcp --gpus t4:4 --use-spot --num-nodes 4 nvidia-smi -c test-spot-mn (skip)

Tested (run the relevant ones):

• Code formatting: bash format.sh
• Any manual or new tests for this PR (please specify below)
• All smoke tests: pytest tests/test_smoke.py
• Relevant individual smoke tests: pytest tests/test_smoke.py::test_fill_in_the_name
  • pytest tests/test_smoke.py::test_gcp_mig
• Backward compatibility tests: bash tests/backward_comaptibility_tests.sh