Bug#837202: pbuilder update no longer works from cron

[Russ Allbery]

Package: pbuilder
Version: 0.226
Severity: important

pbuilder update has started failing when run from cron with the following
error:

tput: No value for $TERM and no -T specified
/usr/lib/pbuilder/pbuilder-modules: line 177: [: -ge: unary operator expected

The bug appears to be here:

term_supports_colors() {
    if [ -z ${USECOLORS:-} ] || [ "$USECOLORS" = "auto" ]; then
        [ $(tput colors) -ge 8 ] && USECOLORS=yes || USECOLORS=no
    fi
}

Looks like tput colors returns an empty string when run with no controlling
terminal, which breaks this conditional.

-- System Information:
Debian Release: stretch/sid
  APT prefers unstable
  APT policy: (990, 'unstable'), (1, 'experimental')
Architecture: amd64 (x86_64)
Foreign Architectures: i386

Kernel: Linux 4.7.0-1-amd64 (SMP w/4 CPU cores)
Locale: LANG=en_US.UTF-8, LC_CTYPE=en_US.UTF-8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash
Init: systemd (via /run/systemd/system)

Versions of packages pbuilder depends on:
ii  debconf [debconf-2.0]  1.5.59
ii  debootstrap            1.0.82
ii  dpkg-dev               1.18.10
ii  wget                   1.18-2+b1

Versions of packages pbuilder recommends:
ii  devscripts  2.16.7
ii  eatmydata   105-3
ii  fakeroot    1.21-2
ii  iproute2    4.6.0-4
ii  net-tools   1.60+git20150829.73cef8a-2
ii  sudo        1.8.17p1-2

Versions of packages pbuilder suggests:
ii  cowdancer   0.80
pn  gdebi-core  <none>

-- debconf information:
  pbuilder/rewrite: false
  pbuilder/nomirror:
  pbuilder/mirrorsite: http://cdn.debian.net/debian