tinycrypt: Rename current tests to avoid confusions with new algorithms

Rename test_ctr to test_ctr_mode to avoid confusions with any CTR-based
algorithm. For example, currently TinyCrypt v0.2.0 supports the
CTR PRNG algorithm.

Rename test_prng to test_hmac_prng to avoid confusions with the test
case for the CTR PRNG algorithm or any test-case related to PRNGs.

Rename test_cbc to test_cbc_mode. TinyCrypt test case for CBC mode is
"test_cbc_mode.c", so it makes sense to keep the same name for the
directory.

Furthermore, README files are also updated to reflect the previous
described changes.

Change-Id: If0af4dcffe8917a7c29608231d3954b73dff5e10
Signed-off-by: Flavio Santes <flavio.santes@intel.com>

tests/crypto/test_cbc_mode/README.txt

@@ -1,4 +1,4 @@
-Title: test_cbc
+Title: test_cbc_mode
 
 Description:
 

tests/crypto/test_ctr_mode/README.txt

@@ -1,8 +1,8 @@
-Title: test_aes
+Title: test_ctr_mode
 
 Description:
 
-This test verifies that the TinyCrypt AES APIs operate as expected.
+This test verifies that the TinyCrypt AES CTR mode APIs operate as expected.
 
 --------------------------------------------------------------------------------
 Building and Running Project:

tests/crypto/test_hmac_prng/README.txt

@@ -1,4 +1,4 @@
-Title: test_prng
+Title: test_hmac_prng
 
 Description:
 

tests/crypto/test_hmac_prng/prj.mdef

@@ -1,4 +1,4 @@
-% Application       : test PRNG TinyCrypt APIs
+% Application       : test HMAC PRNG TinyCrypt APIs
 
 % TASK NAME          PRIO ENTRY           STACK GROUPS
 % ====================================================