TT#29621 Set LC_ALL=C.UTF-8 to fix shellcheck error: hGetContents: invalid argument

shellcheck before version 0.4.7 has an error:
> source/somefile: hGetContents: invalid argument (invalid byte sequence)

The issue is reported and fixed here https://github.com/koalaman/shellcheck/issues/324
Since we are in Jessie and using version 0.3.4 we need to set locale properly.

Change-Id: I92cf75dec4b40d32650375867b97dc7f4ee868a3

t/tap-tests-docker/Dockerfile

@@ -5,7 +5,7 @@ FROM docker.mgm.sipwise.com/sipwise-jessie:latest
 # is updated with the current date. It will force refresh of all
 # of the base images and things like `apt-get update` won't be using
 # old cached versions when the Dockerfile is built.
-ENV REFRESHED_AT 2018-01-04
+ENV REFRESHED_AT 2018-01-05
 
 RUN echo "# generated by Dockerfile from jenkins-tap-test-jessie at $(date)\n\
 deb https://deb.sipwise.com/autobuild/ internal-jessie main\n" > /etc/apt/sources.list.d/sipwise-internal.list
@@ -33,7 +33,10 @@ rm -rf /tmp/zzz
 
 COPY t/tap-tests-docker/perlcriticrc /root/.perlcriticrc
 
-RUN echo 'SHELL=bash WORKSPACE=/code/ /usr/bin/tap_tool_dispatcher' >>/root/.bash_history
+# Set LC_ALL, otherwise shellcheck before v0.4.7 fails:
+# source/somefile: hGetContents: invalid argument (invalid byte sequence)
+# https://github.com/koalaman/shellcheck/issues/324
+RUN echo 'LC_ALL=C.UTF-8 SHELL=bash WORKSPACE=/code/ /usr/bin/tap_tool_dispatcher' >>/root/.bash_history
 
 WORKDIR /code/
 
@@ -52,6 +55,6 @@ WORKDIR /code/
 # % docker run --rm -i -t -v $(pwd):/code/source:rw docker.mgm.sipwise.com/jenkins-tap-test-jessie:latest bash
 #
 # Inside docker (the command is in history, just press UP button):
-#   SHELL=bash WORKSPACE=/code/ /usr/bin/tap_tool_dispatcher
+#   LC_ALL=C.UTF-8 SHELL=bash WORKSPACE=/code/ /usr/bin/tap_tool_dispatcher
 #
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