qa/vstart_runner: increase timeout for vstart.sh command

Since the timeout bug was fixed (https://tracker.ceph.com/issues/65533)
"Ceph API tests" sometimes fails because vstart.sh command had to be
aborted due to timeout.

Currently, "timeout" is set to 300 seconds which sometimes is not enough
for vstart.sh to run successfully for "Ceph API tests" CI job. 180
seconds usually suffices for vstart.sh to run successfully when used for
CephFS.

Increase value of "timeout" to avoid such failures on "Ceph API tests" CI.

Fixes: https://tracker.ceph.com/issues/65565
Signed-off-by: Rishabh Dave <ridave@redhat.com>

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