tools: moveconfig: display log atomically in more readable format

Before this commit, the log was displayed in the format:

<defconfig_name>   : <action1>
<defconfig_name>   : <action2>
<defconfig_name>   : <action3>

When we move multiple CONFIGs at the same time, we see as many
<defconfig_name> strings as actions for every defconfig, which is
redundant information.

Moreover, since normal log and error log are displayed separately,
Messages from different threads could be mixed, like this:

<foo>              : <action1>
<foo>              : <action2>
<bar>              : <action1>
<bar>              : <action2>
<foo>              : <error_log>

This commit makes sure to call "print" once a defconfig, which
enables atomic logging for each defconfig.  It also makes it
possible to refactor the log format as follows:

<foo_defconfig>
    <action1>
    <action2>
    <error_log>

<bar_defconfig>
    <action1>
    <action2>

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Reviewed-by: Joe Hershberger <joe.hershberger@ni.com>