tc-testing: Correct compound statements for namespace execution

If tdc is executing test cases inside a namespace, only the
first command in a compound statement will be executed inside
the namespace by tdc. As a result, the subsequent commands
are not executed inside the namespace and the test will fail.

Example:

for i in {x..y}; do args="foo"; done && tc actions add $args

The namespace execution feature will prepend 'ip netns exec'
to the command:

ip netns exec tcut for i in {x..y}; do args="foo"; done && \
  tc actions add $args

So the actual tc command is not parsed by the shell as being
part of the namespace execution.

Enclosing these compound statements inside a bash invocation
with proper escape characters resolves the problem by creating
a subshell inside the namespace.

Signed-off-by: Lucas Bates <lucasb@mojatatu.com>
Signed-off-by: David S. Miller <davem@davemloft.net>