exec.c: Ignore errors from 'g_io_channel_shutdown'
exec.c: Ignore errors from 'g_io_channel_shutdown'

We do not care about errors from 'g_io_channel_shutdown'. But we
just can't use the same GError we use to store error message
from 'bd_utils_exec_and_report_progress' as it is already used.

rhinstaller/libblockdev,rhinstaller/libblockdev,rhinstaller/libblockdev