Add test for environment.yml + --target-repo-dir

conda sometimes puts stuff in $HOME - specifically under .conda/ -
that might cause package installs to fail due to permission mismatches.

Ref https://github.com/jupyter/repo2docker/issues/604

tests/conda/repo-path/environment.yml

@@ -0,0 +1,2 @@
+dependencies:
+  - numpy

tests/conda/repo-path/verify

@@ -7,4 +7,7 @@ assert sys.executable == '/srv/conda/bin/python'
 
 # Repo should be in /srv/repo
 assert os.path.exists('/srv/repo/verify')
-assert os.path.abspath(__file__) == '/srv/repo/verify'
+assert os.path.abspath(__file__) == '/srv/repo/verify'
+
+# We should be able to import the package in environment.yml
+import numpy