tests: enable networkcache in SR tests

When slapos.libnetworkcache is not installed, then shacache is not
enabled, so SR will no longer build when there's a dead link.

/reviewed on nexedi/slapos!379

software/caddy-frontend/test/setup.py

@@ -38,6 +38,7 @@ setup(name=name,
       packages=find_packages(),
       install_requires=[
         'slapos.core',
+        'slapos.libnetworkcache',
         'erp5.util',
         'requests',
         'forcediphttpsadapter',

software/proftpd/test/setup.py

@@ -43,6 +43,7 @@ setup(name=name,
       packages=find_packages(),
       install_requires=[
         'slapos.core',
+        'slapos.libnetworkcache',
         'erp5.util',
         'pysftp',
         'supervisor',

software/re6stnet/test/setup.py

@@ -43,6 +43,7 @@ setup(name=name,
       packages=find_packages(),
       install_requires=[
         'slapos.core',
+        'slapos.libnetworkcache',
         'erp5.util',
         'supervisor',
         'psutil',