perf test shell: Make perf's inet_pton test more portable

Debian based systems such as Ubuntu have dash as their default shell.
Even if the normal or root user's shell is bash, certain scripts still
call /bin/sh, which points to dash, so we fix this perf test by
rewriting it in a more portable way.

BEFORE:

 $ sudo perf test -v 64
 64: probe libc's inet_pton & backtrace it with ping       :
 --- start ---
 test child forked, pid 31942
 ./tests/shell/record+probe_libc_inet_pton.sh: 18: ./tests/shell/record+probe_libc_inet_pton.sh: expected[0]=ping[][0-9 \.:]+probe_libc:inet_pton: \([[:xdigit:]]+\): not found
 ./tests/shell/record+probe_libc_inet_pton.sh: 19: ./tests/shell/record+probe_libc_inet_pton.sh: expected[1]=.*inet_pton\+0x[[:xdigit:]]+[[:space:]]\(/lib/x86_64-linux-gnu/libc-2.27.so|inlined\)$: not found
 ./tests/shell/record+probe_libc_inet_pton.sh: 29: ./tests/shell/record+probe_libc_inet_pton.sh: expected[2]=getaddrinfo\+0x[[:xdigit:]]+[[:space:]]\(/lib/x86_64-linux-gnu/libc-2.27.so\)$: not found
 ./tests/shell/record+probe_libc_inet_pton.sh: 30: ./tests/shell/record+probe_libc_inet_pton.sh: expected[3]=.*\+0x[[:xdigit:]]+[[:space:]]\(.*/bin/ping.*\)$: not found
 ping 31963 [004] 83577.670613: probe_libc:inet_pton: (7fe15f87f4b0)
 ./tests/shell/record+probe_libc_inet_pton.sh: 39: ./tests/shell/record+probe_libc_inet_pton.sh: Bad substitution
 ./tests/shell/record+probe_libc_inet_pton.sh: 41: ./tests/shell/record+probe_libc_inet_pton.sh: Bad substitution
 test child finished with -2
 ---- end ----
 probe libc's inet_pton & backtrace it with ping: Skip

AFTER:

 $ sudo perf test -v 64
 64: probe libc's inet_pton & backtrace it with ping       :
 --- start ---
 test child forked, pid 32277
 ping 32295 [001] 83679.690020: probe_libc:inet_pton: (7ff244f504b0)
 7ff244f504b0 __GI___inet_pton+0x0 (/lib/x86_64-linux-gnu/libc-2.27.so)
 7ff244f14ce4 getaddrinfo+0x124 (/lib/x86_64-linux-gnu/libc-2.27.so)
 556ac036b57d _init+0xb75 (/bin/ping)
 test child finished with 0
 ---- end ----
 probe libc's inet_pton & backtrace it with ping: Ok

Signed-off-by: Kim Phillips <kim.phillips@arm.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Hendrik Brueckner <brueckner@linux.vnet.ibm.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Michael Petlan <mpetlan@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Sandipan Das <sandipan@linux.vnet.ibm.com>
Cc: Thomas Richter <tmricht@linux.vnet.ibm.com>
Link: http://lkml.kernel.org/r/20180629124643.2089b3ce59960eba34e87b27@arm.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>