explictly use python2, updated health check instruction

Author: mwfarb

webapp/dependencies.md

@@ -46,6 +46,7 @@ webapp \
 - sleep
 - cat
 - systemctl
+- python2
 
 ## SCION Binaries Used/Checked
 - $sbin/scmp

webapp/web/template/health.html

@@ -8,7 +8,8 @@
 
  <h2>SCIONLab Health Check</h2>
  <p>
-  If all automated tests have passed, please continue to <a href="/apps">Apps</a>
+  Click on any test in the list below to read detailed results. If all
+  automated tests have passed, please continue to <a href="/apps">Apps</a>
   in the menu to use SCIONLab.
  </p>
  <ul id="health-list">
@@ -17,7 +18,7 @@ <h2>SCIONLab Health Check</h2>
   <span id="test-complete"></span>
  </p>
  <p>
-  Some tests take a few seconds to succeed, click <a href="/">Health</a>
+  Some tests take a few seconds to complete, click <a href="/">Health</a>
   to test again. Our <a
    href='http://netsec-ethz.github.io/scion-tutorials/general_scion_configuration/troubleshooting'>troubleshooting
    guide</a> may also be useful.

webapp/web/tests/health/netcheck.sh

@@ -10,7 +10,7 @@ as=$(echo ${iaFile} | cut -d"-" -f2)
 topologyFile=$SCION_GEN/ISD$isd/AS$as/endhost/topology.json
 
 # get remote addresses from interfaces
-ip_dsts=$(cat $topologyFile | python -c "import sys, json
+ip_dsts=$(cat $topologyFile | python2 -c "import sys, json
 brs = json.load(sys.stdin)['BorderRouters']
 for b in brs:
     for i in brs[b]['Interfaces']:

webapp/web/tests/health/scmpcheck.sh

@@ -15,7 +15,7 @@ as=$(echo ${iaFile} | cut -d"-" -f2)
 topologyFile=$SCION_GEN/ISD$isd/AS$as/endhost/topology.json
 
 # get remote addresses from interfaces, return paired list
-dsts=($(cat $topologyFile | python -c "import sys, json
+dsts=($(cat $topologyFile | python2 -c "import sys, json
 brs = json.load(sys.stdin)['BorderRouters']
 for b in brs:
     for i in brs[b]['Interfaces']:

webapp/web/tests/health/testVPN.sh

@@ -28,7 +28,7 @@ fi
 ipAddress=$(echo "$targetLines" | grep -oE "\b([0-9]{1,3}\.){3}[0-9]{1,3}\b" | head -n1)
 topologyFile=$SCION_GEN/ISD*/AS*/endhost/topology.json
 # ip address specified in the topology file. If "bind" parameter present, use that one; "public" if not
-ipTopology=$(cat $topologyFile | python -c "import sys, json
+ipTopology=$(cat $topologyFile | python2 -c "import sys, json
 brs = json.load(sys.stdin)['BorderRouters']
 interfaces=next(iter(brs.values()))['Interfaces']
 inter=next(iter(interfaces.values()))