Reduce build log verbosity on Travis
diff --git a/.travis.yml b/.travis.yml
index 2b8eafc1396..89885d08e7b 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -9,6 +9,7 @@ before_install:
 
 before_script:
   - 'if [ $TRAVIS_OS_NAME = osx ] ; then ulimit -n 1024 ; fi'
+  - export TOX_TESTENV_PASSENV=TRAVIS
 
 matrix:
   include:
diff --git a/appveyor.yml b/appveyor.yml
index ce2b5998ce3..2b6b82747a6 100644
--- a/appveyor.yml
+++ b/appveyor.yml
@@ -24,6 +24,7 @@ install:
 build: off
 
 test_script:
+  - set TOX_TESTENV_PASSENV=APPVEYOR
   # Test env is set by TOXENV env variable
   - tox
 
diff --git a/tools/pip_install.py b/tools/pip_install.py
index 354dce32b4c..4466729e03a 100755
--- a/tools/pip_install.py
+++ b/tools/pip_install.py
@@ -71,6 +71,11 @@ def main(args):
     tools_path = find_tools_path()
     working_dir = tempfile.mkdtemp()
 
+    if os.environ.get('TRAVIS'):
+        # When this script is executed on Travis, the following print will make the log
+        # be folded until the end command is printed (see finally section).
+        print('travis_fold:start:install_certbot_deps')
+
     try:
         test_constraints = os.path.join(working_dir, 'test_constraints.txt')
         all_constraints = os.path.join(working_dir, 'all_constraints.txt')
@@ -89,6 +94,8 @@ def main(args):
         call_with_print('"{0}" -m pip install --constraint "{1}" {2}'
                         .format(sys.executable, all_constraints, ' '.join(args)))
     finally:
+        if os.environ.get('TRAVIS'):
+            print('travis_fold:end:install_certbot_deps')
         shutil.rmtree(working_dir)
 
 
diff --git a/tox.ini b/tox.ini
index 021c2394942..71491c34afc 100644
--- a/tox.ini
+++ b/tox.ini
@@ -64,9 +64,6 @@ source_paths =
     tests/lock_test.py
 
 [testenv]
-passenv = 
-    TRAVIS
-    APPVEYOR
 commands =
     {[base]install_and_test} {[base]all_packages}
     python tests/lock_test.py
@@ -176,7 +173,6 @@ whitelist_externals =
     docker
 passenv =
     DOCKER_*
-    TRAVIS
 
 [testenv:nginx_compat]
 commands =
@@ -187,7 +183,6 @@ whitelist_externals =
     docker
 passenv =
     DOCKER_*
-    TRAVIS
 
 [testenv:le_auto_precise]
 # At the moment, this tests under Python 2.7 only, as only that version is
@@ -199,7 +194,6 @@ whitelist_externals =
     docker
 passenv =
     DOCKER_*
-    TRAVIS
 
 [testenv:le_auto_trusty]
 # At the moment, this tests under Python 2.7 only, as only that version is
@@ -212,7 +206,6 @@ whitelist_externals =
     docker
 passenv =
     DOCKER_*
-    TRAVIS
     TRAVIS_BRANCH
 
 [testenv:le_auto_wheezy]

PR #6568 removed the `--quiet` option in pip invocations, because this option deletes a lot of extremely useful logs when something goes wrong. However, when everything goes right, or at least when pip install is correctly executed, theses logs add hundreds of lines that are only noise, making hard to debug errors that can be in only one or two lines.

We can have best of both worlds. Travis allows to fold large blocks of logs, that can be expanded directly from the UI if needed. It only requires to print in the console some specific code, that this PR implements in the `pip_install.py` script when the build is run in Travis (known by the existence of `TRAVIS` environment variable).

I also take the occasion to clean up a little `tox.ini`.

Note that AppVeyor does not have this fold capability, but it can be emulated using a proper capture of stdout/stderr delivered only when an error is detected.