printk() support for the '-' indicator in format string (left justifier)

[nashif]

Reported by Tomasz Bursztyka:

For instance:

printk("%-8u", a_number);

For now, only printf() supports it, but in some shell modules, having a nice output is necessary (a lot of complex information can be written, and it's all worse if everything is not nicely formated). And since printk() is preferred (lighter than printf etc...), it would be nice to get that support in printk.

(Imported from Jira ZEP-1599)

[nashif]

by Sharron LIU:

test case under review and merge.
zephyrproject-rtos/zephyr#25

verified printk left justifier passed at all qemu platforms (@qemu_x86, @qemu_cortex_m3, @qemu_rescv32, @qemu_nios2). Closing this. Thanks.

NOTE: the test @qemu_cortex_m3 build failed due to recent changes at DTS. This's not related to this story. It is a different issue, logged as GH-1928.