tests: Rename test suits not following the test suite naming convention

The name of the fixture test suite in `src/test/foo_tests.cpp`
should be `foo_tests`.

src/test/blockchain_tests.cpp

@@ -54,7 +54,7 @@ void TestDifficulty(uint32_t nbits, double expected_difficulty)
     RejectDifficultyMismatch(difficulty, expected_difficulty);
 }
 
-BOOST_FIXTURE_TEST_SUITE(blockchain_difficulty_tests, BasicTestingSetup)
+BOOST_FIXTURE_TEST_SUITE(blockchain_tests, BasicTestingSetup)
 
 BOOST_AUTO_TEST_CASE(get_difficulty_for_very_low_target)
 {

src/test/prevector_tests.cpp

@@ -13,7 +13,7 @@
 
 #include <boost/test/unit_test.hpp>
 
-BOOST_FIXTURE_TEST_SUITE(PrevectorTests, TestingSetup)
+BOOST_FIXTURE_TEST_SUITE(prevector_tests, TestingSetup)
 
 template<unsigned int N, typename T>
 class prevector_tester {

src/wallet/crypter.h

@@ -67,7 +67,7 @@ public:
 
 typedef std::vector<unsigned char, secure_allocator<unsigned char> > CKeyingMaterial;
 
-namespace wallet_crypto
+namespace crypto_tests
 {
     class TestCrypter;
 }
@@ -75,7 +75,7 @@ namespace wallet_crypto
 /** Encryption/decryption context with key information */
 class CCrypter
 {
-friend class wallet_crypto::TestCrypter; // for test access to chKey/chIV
+friend class crypto_tests::TestCrypter; // for test access to chKey/chIV
 private:
     std::vector<unsigned char, secure_allocator<unsigned char>> vchKey;
     std::vector<unsigned char, secure_allocator<unsigned char>> vchIV;

src/wallet/test/coinselector_tests.cpp

@@ -13,7 +13,7 @@
 #include <boost/test/unit_test.hpp>
 #include <random>
 
-BOOST_FIXTURE_TEST_SUITE(coin_selection_tests, WalletTestingSetup)
+BOOST_FIXTURE_TEST_SUITE(coinselector_tests, WalletTestingSetup)
 
 // how many times to run all the tests to have a chance to catch errors that only show up with particular random shuffles
 #define RUN_TESTS 100

src/wallet/test/crypto_tests.cpp

@@ -10,7 +10,7 @@
 
 #include <boost/test/unit_test.hpp>
 
-BOOST_FIXTURE_TEST_SUITE(wallet_crypto, BasicTestingSetup)
+BOOST_FIXTURE_TEST_SUITE(crypto_tests, BasicTestingSetup)
 
 class TestCrypter
 {