vmm: relax resume_vcpus's timeout
vmm: relax resume_vcpus's timeout

Starting 100 VMs on a EC2 m5d.metal host sometimes didn't work due to
the timeout.

Fixes #1555.

Signed-off-by: Kazuyoshi Kato <732288c132d39c7d9231a005036e5ecd0fff1d64@amazon.com>

firecracker-microvm/firecracker,firecracker-microvm/firecracker,firecracker-microvm/firecracker,firecracker-microvm/firecracker,firecracker-microvm/firecracker