better clean up of created namespace/interfaces if ctrl-c is pressed
better clean up of created namespace/interfaces if ctrl-c is pressed

  o There are still some cases when ctrl-c is pressed, the program does not exit
    gracefully, with a however lower probability. In my random manual experiments,
    one in ten cases it still hangs and needs further ctrl-z.

Signed-off-by: Yonghong Song <e76892bbe783db2f627de1232e139db4de43da60@plumgrid.com>

romain-intel/bcc,brendangregg/bcc,mshahbaz/bcc-deprecated,bpowers/bcc,mshahbaz/bcc-deprecated,mbudiu-bfn/bcc,arslanabbasi/bcc,bpowers/bcc,mkacik/bcc,zaafar/bcc,iovisor/bcc,shodoco/bcc,mshahbaz/bcc-deprecated,mshahbaz/bcc-deprecated,zaafar/bcc,tuxology/bcc,romain-intel/bcc,bpowers/bcc,mcaleavya/bcc,arslanabbasi/bcc,bpowers/bcc,brendangregg/bcc,mcaleavya/bcc,zaafar/bcc,mkacik/bcc,romain-intel/bcc,romain-intel/bcc,mbudiu-bfn/bcc,mcaleavya/bcc,iovisor/bcc,iovisor/bcc,mkacik/bcc,shodoco/bcc,brendangregg/bcc,zaafar/bcc,tuxology/bcc,zaafar/bcc,shodoco/bcc,mkacik/bcc,mcaleavya/bcc,mbudiu-bfn/bcc,bpowers/bcc,iovisor/bcc,brendangregg/bcc,mcaleavya/bcc,mbudiu-bfn/bcc,tuxology/bcc,shodoco/bcc,arslanabbasi/bcc,romain-intel/bcc,tuxology/bcc,brendangregg/bcc,mkacik/bcc,iovisor/bcc,shodoco/bcc,arslanabbasi/bcc,arslanabbasi/bcc,mshahbaz/bcc-deprecated,mbudiu-bfn/bcc,tuxology/bcc