Turn of ntpd and set date manually before tests

This should fix the problem where we see the first test
taking negative time, as well as possibly other issues
with performance tests which may be sensitive to changes
in wall clock time.

Fixes #398

util/vm/build.py

@@ -484,6 +484,15 @@ def login( vm, user='mininet', password='mininet' ):
     log( '* Waiting for login...' )
 
 
+def disableNtpd( vm, prompt=Prompt, ntpserver='pool.ntp.org' ):
+    "Turn off ntpd and set clock from pool.ntp.org"
+    log( '* Turning off ntpd' )
+    vm.sendline( 'sudo -n service ntp stop' )
+    vm.expect( prompt )
+    log( '* Setting clock from', ntpserver  )
+    vm.sendline( 'sudo -n ntpdate ' + ntpserver )
+
+
 def sanityTest( vm ):
     "Run Mininet sanity test (pingall) in vm"
     vm.sendline( 'sudo mn --test pingall' )
@@ -802,6 +811,10 @@ def build( flavor='raring32server', tests=None, pre='', post='', memory=1024 ):
 
 def runTests( vm, tests=None, pre='', post='', prompt=Prompt ):
     "Run tests (list) in vm (pexpect object)"
+    # We disable ntpd and set the time so that it won't be
+    # messing with the time during tests
+    disableNtpd( vm )
+    vm.expect( prompt )
     if Branch:
         checkOutBranch( vm, branch=Branch )
         vm.expect( prompt )