Work around intermittent test failure where gdb just forgets to process a command in a list of multiple commands

See https://buildkite.com/julialang/rr/builds/1439#018ae9dd-9eb5-4f02-87ea-dfb3804edbc6
We issue these commands without waiting
 cond 1 v2*v2==4
 cond 2 !(v2*v2==4)
 c
Gdb does
 (rr) cond 1 v2*v2==4
 (rr) cond 2 !(v2*v2==4)
 (rr)
and then just hangs without executed the "c".

This commit uses the Python interpreter to do all 3 commands in one input line. Seems to fix the problem.

Author: rocallahan

src/test/breakpoint_conditions.py

@@ -1,11 +1,7 @@
 from util import *
 
 def test_cond(c):
-    send_gdb('cond 1 %s'%c)
-    # check that the condition is evaluated correctly by checking that
-    # we don't break on the negation of the condition
-    send_gdb('cond 2 !(%s)'%c)
-    send_gdb('c')
+    send_gdb('python gdb.execute("cond 1 %s"); gdb.execute("cond 2 !(%s)"); gdb.execute("c")' % (c, c))
     expect_gdb('Breakpoint 1')
 
 send_gdb('b breakpointA')