CircleCI: Do not run build as root. Move to public docker repo.

Change docker hub repository to 'openwrtorg'.
Create and use non-root user 'build'. Add xz-utils and unzip.
Use version numbers for docker images (SHA has no sense of time).
Disable pipefail in build step

Signed-off-by: Ted Hess <thess@kitschensync.net>

.circleci/Dockerfile

@@ -14,8 +14,14 @@ subversion \
 time \
 wget \
 zlib1g-dev \
+unzip \
+xz-utils \
 && rm -rf /var/lib/apt/lists/*
 
+RUN useradd -c "OpenWrt Builder" -m -d /home/build -s /bin/bash build
+USER build
+ENV HOME /home/build
+
 # LEDE Build System (LEDE GnuPG key for unattended build jobs)
 RUN curl 'https://git.openwrt.org/?p=keyring.git;a=blob_plain;f=gpg/626471F1.asc' | gpg --import \
  && echo '54CC74307A2C6DC9CE618269CD84BCED626471F1:6:' | gpg --import-ownertrust