ms_srs: import numpy module on first use

Change-Id: I2ce974954028bdbc7bc1561c4538b909edee2cb1

src/osmo_gsm_tester/obj/ms_srs.py

@@ -343,8 +343,6 @@ class srsUE(MS):
         metrics = srsUEMetrics(self.metrics_file)
         return metrics.verify(value, operation, metric, criterion)
 
-import numpy
-
 class srsUEMetrics(log.Origin):
 
     VALID_OPERATIONS = ['avg', 'sum']
@@ -357,6 +355,7 @@ class srsUEMetrics(log.Origin):
         super().__init__(log.C_RUN, 'srsue_metrics')
         self.raw_data = None
         self.metrics_file = metrics_file
+        import numpy
         # read CSV, guessing data type with first row being the legend
         try:
             self.raw_data = numpy.genfromtxt(self.metrics_file, names=True, delimiter=';', dtype=None)