[DOC] Correct requirements for doc chain building

- Remove unecessary requirements
- It leverages the latest lfdocs-conf (0.7.7) updates
- It now loads all centralized upper contraints from ONAP doc
- Correct conf.py to use app.add_css_file()

Issue-ID: DOC-765

Signed-off-by: Eric Debeau <eric.debeau@orange.com>
Change-Id: Ie8aa095bc9ac263a754734ea7d9bfff427ddcca0
diff --git a/docs/tox.ini b/docs/tox.ini
index edac8c3..811bb5e 100644
--- a/docs/tox.ini
+++ b/docs/tox.ini
@@ -1,11 +1,14 @@
 [tox]
 minversion = 1.6
-envlist = docs,
+envlist = docs
 skipsdist = true
 
 [testenv:docs]
 basepython = python3
-deps = -r{toxinidir}/requirements-docs.txt
+deps =
+    -r{toxinidir}/requirements-docs.txt
+    -chttps://git.onap.org/doc/plain/etc/upper-constraints.os.txt
+    -chttps://git.onap.org/doc/plain/etc/upper-constraints.onap.txt
 commands =
     sphinx-build -b html -n -d {envtmpdir}/doctrees ./ {toxinidir}/_build/html
     echo "Generated docs available in {toxinidir}/_build/html"
@@ -16,7 +19,10 @@
 
 [testenv:docs-linkcheck]
 basepython = python3
-#deps = -r{toxinidir}/requirements-docs.txt
+deps =
+    -r{toxinidir}/requirements-docs.txt
+    -chttps://git.onap.org/doc/plain/etc/upper-constraints.os.txt
+    -chttps://git.onap.org/doc/plain/etc/upper-constraints.onap.txt
 commands = echo "Link Checking not enforced"
 #commands = sphinx-build -b linkcheck -d {envtmpdir}/doctrees ./ {toxinidir}/_build/linkcheck
 whitelist_externals = echo