pkg-utils: mask tput failure for non-interactive sessions

When invoking a build from a non-interactive session (for example, a
Jenkins build), there is no terminal session to modify. When preparing
variables to track the bold and boldoff mode sequences, the `tput`
command will always fail as there is no terminal to query. The following
change masks the error message when `tput` fails; leaving the TERM_BOLD
and TERM_RESET variables empty.

Signed-off-by: James Knight <james.d.knight@live.com>
Acked-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>