Make zimport.sh bash dependency explicit

Unfortunately, the zimport.sh test script really does depend on
bash.  Moving to /bin/sh should be possible once the shared
infrastructure scripts it depends on is made portable.

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>

scripts/zimport.sh

@@ -1,4 +1,4 @@
-#!/bin/sh
+#!/bin/bash
 #
 # Verify that an assortment of known good reference pools can be imported
 # using different versions of the ZoL code.