Fix race conditions

[anupcshan]

Vnode and localVnode currently has very little locking in place. Consequently, calling RPC methods concurrently leads to race conditions. Fix them!

Test:
go test -v github.com/buddyfs/buddystore -race

Currently shows 193 (this number is flaky) failures, and the test sometimes fails outright in -race mode because artifacts are not being cleaned up at the end of tests.

[anupcshan]

After some amount of bug squashing, we're now down to somewhere between 35 and 45 race conditions as observed by the Go race detector. Here's a summary of the tests which still show races:

Test	Races
TestLeave	14
TestLookup	6
TestJoin	4
TestJoinLockRemote	4
TestTrackerIntegrationJoinRing	3
TestKVIntegrationCreateThenGetKey	2
TestTrackerIntegrationTCPTransportTest	2
TestGlobalReplication	1
TestKVIntegrationTCPTransportTest	1
TestRingSchedule	1
TestRLockInvalidate	1
TestWLockTimeTicker	1

Here is the command I used to look at per test races:
for test in grep -o 'func .\s(t *testing.T' _test.go | sed "s/.func (.)\s(t.*/\1/"; do echo "Testing $test"; go test -v ./... -timeout 20s -run $test -race 2>&1 | grep 'data race'; sleep 1; done

[anupcshan]

Updated list of races:

Test	Races
TestJoinLockRemote	1
TestGlobalReplication	1
TestRingSchedule	1
TestTrackerIntegrationJoinRing	1
TestTrackerIntegrationTCPTransportTest	1

[narendran]

All race conditions have been fixed.