Mnt/update fsl package

Fixes to update_fsl_package script, and updates to unit tests to get them running

share/fsl/sbin/update_fsl_package

@@ -88,9 +88,24 @@ def conda(cmd : str, capture_output=True, **kwargs) -> str:
 
     Keyword arguments are passed through to subprocess.run.
     """
+
     fsldir   = os.environ['FSLDIR']
     condabin = op.join(fsldir, 'bin', 'conda')
 
+    # If FSLDIR is a child env, we won't be able
+    # to find the conda executable. In this case,
+    # we have to assume  that we can call "conda".
+    candidates = [
+        op.join(fsldir, 'bin',      'conda'),
+        op.join(fsldir, 'condabin', 'conda'),
+    ]
+
+    for condabin in candidates:
+        if op.exists(condabin):
+            break
+    else:
+        condabin = 'conda'
+
     log.debug(f'Running {condabin} {cmd}')
 
     kwargs['check']          = False